P0C8E: Sensor J temperature disagrees with the battery's other sensors

P0C8E identifies hybrid/EV battery temperature sensor J range/performance. The 2018 GM monitor compares J's reported temperature with an average of other battery-temperature sensors. Either a warmer or a colder disagreement can fail because the test uses the absolute difference.

A relative temperature test

The documented discrepancy threshold is more than 25 °C. Fifty failed samples out of 67, at 25-millisecond intervals, meet the listed 1.675-second evaluation. GM classifies the monitor Type B, two trips.

Specified low-circuit, high-circuit, erratic-signal and battery-interface communication faults inhibit this comparison. The controller therefore needs credible supporting inputs before assessing J's plausibility. A passing electrical range check alone does not guarantee that J agrees with the rest of the measurements.

Interpreting a disagreement

Preserve J's reading and the other temperature inputs together. The code establishes disagreement, not which measurement is necessarily correct. A single J reading without the comparison data loses the central evidence. It also does not prove that the complete battery is overheating.

A technician should establish the vehicle's sensor mapping and investigate the discrepancy using the appropriate thermal and circuit checks. After repair, verify that the comparison is enabled and passes; no new code while an inhibiting fault remains is inconclusive. Internal battery access requires qualified high-voltage service. The table does not supply a universal physical location for sensor J.

Source and applicability

This explanation follows the documented GM monitor, not a verified application to every vehicle with this code. Confirm the vehicle, reporting module and calibration in current service information. GM diagnostic table, physical page 917.